Yoshihiro Oshida

Strain distribution measuring system using speckle shearing interferometer

A strain distribution measuring system using a phase-shifting speckle shearing interferometer is proposed. A strain is obtained by the spatial differentiation of the in-plane component of the deformation on the object surface. In this interferometer, the spatial differentiation is performed optically by the interference with two sheared images formed by the diffraction grating in the imaging arrangements. The phase change of the interfering speckle between before and after deformation corresponds to the spatial differentiation of the deformation, i.e., the strain of the object surface. Moreover, in order to measure the phase change accurately, a 4-step phase-shifting method is adopted in our method. The phase-shifting is achieved by moving a diffraction grating. Hence two diffraction gratings are used for spatial shearing and a phase-shifting. As the phase change is calculated by a 4-step phase-shifting method at every point of object surface, the strain distribution can be obtained. The strain is the spatial differentiation of the in-plane component of the deformation, so this component should be measured. In order to measure this component, we illuminate the object surface from two directions which are symmetric with respect to the normal of the object surface. In this method, the calculation of the phase change is performed every illuminating directions independently, so two independent laser sources are used for two illuminating lights. The experimental result measuring the strain of the cantilever shows the validity of this measuring system. Using this system, a miniaturization and a practical application of the measuring system is anticipated.

Development of an optical ruler for range finding using a binary Fresnel hologram

We propose an optical ruler for range finding using a Fresnel hologram which can project several different diffraction images depending on the imaging distance. The distance resolution equivalent to the scale width of a ruler was obtained by computer simulation. The optical ruler was fabricated using electron beam lithography. The fabricated optical ruler acted on a ruler for range finding with distance resolution of 20 millimeters.

Visualization of ultrasonic wave fronts using holographic interferometry

Holographic interferometry with a phase-modulated reference beam is used to visualize a progressive ultrasonic wave in the interior of a transparent medium. The medium is illuminated with sheetlike light, and the light scattered from the plane of the light sheet is recorded in the hologram. The ultrasonic field on the plane is obtained from the reconstructed image, which provides the equiphase positions of the wave, i.e., wave fronts. Experiments were performed at 200-kHz frequency. The effect of flow in the medium is estimated. An analysis of the optical system suggests that this method is applicable to ultrasonic waves with frequencies up to ~6 MHz.

Visualization of Three-Dimensional Ultrasonic Wave Fronts Using Holographic Interferometry

A new method to visualize wave fronts of a 3-D ultrasonic wave in a transparent medium is proposed. It employs holographic interferometry with phase-modulated reference beam. The wave field is illuminated by a sheet-like light and the light scattered in the medium is recorded in a hologram. The reconstructed image displays wave fronts of the ultrasound on the light sheet. The experiments are carried out for an ultrasonic wave with frequency 200 kHz and 1 MHz, and prove the validity of the method. This method is considered applicable for an ultrasonic wave with frequency up to about 10 MHz.

Visualization of High Frequency Ultrasonic Wavefronts by Holographic Interferometry

[7 ] D. L. Folds and D. C. Loggins, “Transmission and reflection of [8] L. E. Kinsler and A. R. Frey, Fundamentals ofAcoustics, 2nd Ed. New York: Wiley, 1962. D. 226. [9] E. P. Papadakis, K. A. Fowler, and L. C. Lynnworth, “Ultrasonic attenuation by spectrum analysis of pulses in buffer rods: method and diffraction corrections,” J. Acousr. Soc. Am., vol. 53, no. 5, pp. 1336-1343, 1973. [ 101 M. Perdrix, J. C. Baboux, and F. Lakestani, “Etude thkorique et expkrimentale de la couche de couplant sur la rkponse d’un transducteur ultrasonore large bande,” J. Phys. D: Appl. Phys., vol. 13, pp. 185-194, 1980.

Speckle shearing interferometer for measuring strain distribution using laser diodes

We have been proposed a phase shifting speckle shearing interferometer using a diffraction grating for measuring the strain distribution. A strain is obtained by the spatial differentiation of the in-plane component of the deformation. In this system, to measure the in-plane component of the object deformation, the object surface is illuminated in two symmetrical directions about the normal of the object surface. Moreover, the spatial differentiation of the in-plane deformation and phase-shifting are achieved by the diffraction grating. However, the object surface is illuminated by a He-Ne laser in the conventional method, and the illuminating direction is changed by switching the optical path mechanically. Then, we use laser diodes as a light source which has high power and is small size. But, coherency of laser diode is low. In this method, as common path arrangements are used, the path difference is so small that sheared speckles interfere each other. Therefore, the laser diode can be applicable for this measuring system. Additionally, in order to illuminate the object from two directions, two independent laser diodes are used. So, the optical path change is performed electrically. The strain distribution of the bending cantilever is measured with this two laser diodes method. The measured result coincides with theoretical value qualitatively. Therefore the experimental results show the validity of this method.

Measurement of spatial differentiation of displacement using a phase-shifting speckle shearing interferometer

A phase-shifting speckle shearing interferometer using a TV camera and a. computer to measure the spatial differentiated data. of the displacement is presented. In this method a spatial differentiation is achieved optically by the diffraction grating. This grating is also used,for phase-shifting. The distribution of the differentiated data is obtained accurately without contact with the object.